BEIJING - Chinese authorities investigating what could be Beijing's first major suicide attack searched on Tuesday for two men from Muslim-dominated Xinjiang after three people suspected to be from the restive region drove an SUV into a crowd at Tiananmen Square and set it on fire.

They killed themselves and two tourists on Monday in the square, the heart of China's power structure and the focal point of the mass 1989 pro-democracy demonstrations brutally crushed the military.

Police have spread a dragnet across the capital, checking hotels and vehicles, seeking two people suspected to be ethnic Uighurs, a Muslim minority from Xinjiang in China's far west, on the borders of former Soviet Central Asia.

Two senior sources said on Tuesday the crash, which also injured 38 bystanders at perhaps the most closely guarded location in China, was suspected of being a suicide attack carried out by people from Xinjiang. It was initially believed to be an accident.

The sources did not specifically say the occupants were Uighurs, many of whom chafe at Chinese controls on their culture and religion.

"It looks like a pre-meditated suicide attack," said a source with direct knowledge of the matter, speaking on condition of anonymity to avoid repercussions for talking to the foreign media.

There have been suicide bombings before in China, and in Beijing, mostly by people with personal grievances, but none have targeted the very heart of China's government like this appears to have.

China has blamed Uighur separatists and religious extremists for a series of attacks in Xinjiang, saying they want to establish an independent state called East Turkestan. Rights groups and exiles say China massively overstates the threat.

In 2009, nearly 200 people were killed in clashes between Uighurs and ethnic Chinese in Urumqi, the capital of Xinjiang. But the unrest has never before spilled over into China's capital despite speculation in 1997 that Uighurs were to blame for a Beijing bus bomb that killed at least two people.

Uighurs are also not known to have previously carried out suicide attacks.